package main

import (
	"image"
	"image/color"
	"image/gif"
	"io"
	"time"
	"math"
	"math/rand"
	"os"
)

var palette = []color.Color{color.White, color.Black}

const (
	whiteIndex = 0
	blackIndex = 1
)

func main(){
	rand.Seed(time.Now().UTC().UnixNano())
	lissajous(os.Stdout)
}

func lissajous(out io.Writer){
	const(
		cycles = 5     //
		res    = 0.001
		size   = 100
		nframes= 64
		delay  = 8
		)

	freq := rand.Float64() * 3.0
	anim := gif.GIF{LoopCount:nframes}
	phase:= 0.0
	for i:=0; i < nframes; i++ {
		rect := image.Rect(0, 0, 2 * size, 2 * size + 1) //长方形
		img  := image.NewPaletted(rect, palette)

		for t := 0.0; t < cycles * 2 * math.Pi; t += res {
			x := math.Sin(t)
			y := math.Sin(t * freq + phase)
			img.SetColorIndex(size + int(x * size + 0.5), size + int(y*size + 0.5), blackIndex)
		}

		phase += 0.1
		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}

	gif.EncodeAll(out, &anim)
}